Arctic sea ice extent reached 5.61 million square miles on February 25, and then began to retreat. Unless a late growth spurt takes place, it will be the smallest winter maximum in the satellite record.

Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Climate scientists are wondering if a warmer Arctic could explain its odd behavior in recent years.

Averaged over September 2013, sea ice extent was 2.07 million square miles—larger than last year's record low, but still more than 17 percent below average and the sixth smallest September extent on record.

To be consistent with NOAA's use of 30-year periods for the official "climate normals," the National Snow and Ice Data Center switched its baseline period for sea ice analyses from 1979-2000 to 1981-2010. Compared to the new normal, the low ice conditions of the recent past will appear less abnormal than they used to.